can we only use "lo suyo" if it refers to something mentioned before? ie we cannot say "eso sería lo suyo" as a stand alone sentence?
Yes, you don't always have to use it to refer to something just mentioned or implicit in the conversation. Sometimes, as we say in the lesson in one of the bullet points is used to express something like "the right thing to do..." which is what you express in the sentence you gave us:
"Eso sería lo suyo"
That'd be ideal (the right/ideal thing)
Sign in to submit your answer
Don't have an account yet? Join today
Test your Spanish to the CEFR standard